Coinmercial Electron Microscopes 



1Z 



Slow fluctuations, that is, slow in comparison with 32 kilo- 

 cycles, are suppressed \)\ an inverse feedback regulator.''" The 

 principle is indicated in figure 21. The high voltage output is 

 divided by a potentiometer, which, it may be mentioned, takes a 



s.?A,l^im.^mM^i^ 



Fig. 22. Preparation of specimens for the R.C.A. electron microscope 



current considerably larger than the maximum 0.5 millamperes 

 of the discharge tube, so that the rectifier works under rather 

 steady current conditions. The divided voltage is balanced 

 against a dry battery. (CJrdinary anode batteries fluctuate by 

 less than three parts in a million during 30 second intervals.) 

 The voltage difiference is amplified by a d-c amplifier, and the 



